This application is based upon and claims the benefit of Japanese Patent Application No. 2001-171497 filed on Jun. 6, 2001 and No. 2002-9817 filed on Jan. 18, 2002, the contents of which are incorporated herein by reference.
The present invention relates to an electrical device having bonding pads that is bonded with metal wiring and a manufacturing method thereof.
An electrical device such as the device shown in FIGS. 11A, 11B includes a substrate 10, which is made of ceramics or the like. Pads 22 for connecting to electrical parts or for bonding with wiring are formed on a first surface 11 and a second surface 12. The pads 22 include W (tungsten) layers 22a as base layers and Cu (cupper) plating layers 22b thereon. Regarding the pads 22 on the second surface 12, resistors 72 constructed by thick layers are formed through Cu thick layers 70. Further, a passivating glass 74 and a passivating resin 76 are respectively formed to cover the resistors 72, the Cu thick layers 70 and the pads 22.
Next, as shown in FIG. 11B, IC tips 30, 55 and other electrical parts 40 such as capacitors or the like are connected to the pads 22 formed on the first surface 11 by using solder 41, 51 and a conductive adhesive 31. Thereafter, the pads 22 are electrically connected to the IC tips 30, 55 via Au wiring 60 or Al wiring 61.
However, in the above-mentioned method, the heat used to melt the solder 41, 51 or for hardening the conductive adhesive 31 oxidizes the exposed Cu plating layers 22b of the pads 22 that are formed on the first surface 11. Therefore, a bonding force between the wiring 60, 61 and the Cu plating layers 22b decreases.
Alternatively, JP-A-2000-58745 discloses that Ni plating layer and Au plating layer are deposited on Cu conductive wiring in this order on a resin board. In this construction, oxidization of the Cu conductive wiring can be prevented. Further,Cu diffusion from the Cu conductive wiring to the Au plating layer decreases.
However, though the Cu in the Cu conductive wiring is a flexible material, it is possible that ultrasonic waves can be more easily transmitted during wire bonding because Ni is solid material. In addition, in the above-mentioned Cuxe2x80x94Nixe2x80x94Au construction, a battery effect occurs between the Ni plating layer and the Au plating layer due to water in a humid environment. Therefore, corrosion by products such as NiOH or the like are generated, thereby possibly separating the bonding wiring from the pad.
It is therefore an object of the present invention to provide an electrical device having a metal pad bonded with metal wiring that is capable of obviating the above problem.
It is another object of the present invention to provide a metal pad that is capable of repressing separation of the metal wiring.
If a two-layer plating structure having a Cu plating layer and Au plating layer directly thereon is used as a pad, it is able to prevent the Cu plating layer from oxidizing because of the Au plating layer. Further, corrosion by products that would be generated between the Ni plating layer and the Au plating layer are not generated because the Ni plating layer is not used.
Accordingly, in this invention, a substrate has a first surface and a second surface. A plurality of pads is formed on the first surface. Further, each pad has a Cu plating layer and an Au plating layer that is directly formed on the Cu plating layer.
However, when the Al wiring is used as metal wiring, a Kirkendall void is generated between the Au plating and the Al wiring under a high temperature environment, thereby also separating the bonding wiring from the pad.
It is considered that the Kirkendall void is generated because a diffusion speed of Au under high temperature is much faster than that of the other metal materials, for example, Al, Cu. Namely, Au deficient portions are generated in the Au plating layer, thereby forming the Kirkendall void. Incidentally, regarding the three-layer construction having the Cu conductive wiring, the Ni plating layer and Au plating layer, the Kirkendall void is hard to generate because Au cannot diffuse due to a barrier layer of Ni plating.
Accordingly, in this present invention, the thickness of the Au plating layer that is bonded with the Al wiring is less than 0.5 xcexcm.
Further, in case that the Al wiring is used as metal wiring, it possible that the wiring bonding separates from the pad if the Au plating layer is too thin.
Accordingly, the thickness of the Au plating layer that is bonded with the Au wiring is 0.05 xcexcm or more.